High Strength, High Toughness  Steel Alloy

ABSTRACT

A high strength, high toughness steel alloy is disclosed. The alloy has the following broad weight percent composition. 
     
       
         
               
               
               
             
                   
                   
               
                   
                 Element 
                 Broad 
               
                   
                   
               
                   
                 C 
                 0.35-0.55 
               
                   
                 Mn 
                 0.6-1.2 
               
                   
                 Si 
                 0.9-2.5 
               
                   
                 P 
                 0.01 max. 
               
                   
                 S 
                 0.001 max.  
               
                   
                 Cr 
                 0.75-2.0  
               
                   
                 Ni 
                 3.5-7.0 
               
                   
                 Mo + ½ W 
                 0.4-1.3 
               
                   
                 Cu 
                 0.5-0.6 
               
                   
                 Co 
                 0.01 max. 
               
                   
                 V + ( 5/9) × Nb 
                 0.2-1.0 
               
                   
                 Fe 
                 Balance 
               
                   
                   
               
           
              
              
              
             
             
              
              
              
              
              
              
              
              
              
              
              
              
              
             
          
         
       
     
     Included in the balance are the usual impurities found in commercial grades of steel alloys produced for similar use and properties. Also disclosed is a hardened and tempered article that has very high strength and fracture toughness. The article is formed from the alloy having the broad weight percent composition set forth above. The alloy article according to this aspect of the invention is further characterized by being tempered at a temperature of about 500° F. to 600° F.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority from U.S. Provisional Application No.61/083,249, filed Jul. 24, 2008 and U.S. Provisional Application No.61/172,098, filed Apr. 23, 2009, the entireties of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to high strength, high toughness steel alloys,and in particular, to such an alloy that can be tempered at asignificantly higher temperature without significant loss of tensilestrength. The invention also relates to a high strength, high toughness,tempered steel article.

2. Description of the Related Art

Age-hardenable martensitic steels that provide a combination of veryhigh strength and fracture toughness are known. Among the known steelsare those described in U.S. Pat. No. 4,706,525 and U.S. Pat. No.5,087,415. The former is known as AF1410 alloy and the latter is soldunder the registered trademark AERMET. The combination of very highstrength and toughness provided by those alloys is a result of theircompositions which include significant amounts of nickel, cobalt, andmolybdenum, elements that are typically among the most expensivealloying elements available. Consequently, those steels are sold at asignificant premium compared to other alloys that do not contain suchelements.

More recently, a steel alloy has been developed that provides acombination of high strength and high toughness without the need foralloying additions such as cobalt and molybdenum. One such steel isdescribed in U.S. Pat. No. 7,067,019. The steel described in that patentis an air hardening CuNiCr steel that excludes cobalt and molybdenum. Intesting, the alloy described in the '019 patent has been shown toprovide a tensile strength of about 280 ksi together with a fracturetoughness of about 90 ksi √in. The alloy is hardened and tempered toachieve that combination of strength and toughness. The temperingtemperature is limited to not more than about 400° F. in order to avoidsoftening of the alloy and a corresponding loss of strength.

The alloy described in the '019 patent is not a stainless steel andtherefore, it must be plated to resist corrosion. Materialspecifications for aerospace applications of the alloy require that thealloy be heated at 375° F. for at least 23 hours after being plated inorder to remove hydrogen adsorbed during the plating process. Hydrogenmust be removed because it leads to embrittlement of the alloy andadversely affects the toughness provided by the alloy. Because thisalloy is tempered at 400° F., the 23 hour 375° F. post-plating heattreatment results in over-tempering of parts made from the alloy suchthat a tensile strength of at least 280 ksi cannot be provided. It wouldbe desirable to have a CuNiCr alloy that can be hardened and tempered toprovide a tensile strength of at least 280 ksi and a fracture toughnessof about 90 ksi √in, and maintain that combination of strength andtoughness when heated at about 375° F. for at least 23 hours, subsequentto being hardened and tempered.

SUMMARY OF THE INVENTION

The disadvantages of the known alloys as described above are resolved toa large degree by an alloy according to the present invention. Inaccordance with one aspect of the present invention, there is provided ahigh strength, high toughness steel alloy that has the following broadand preferred weight percent compositions.

Element Broad Preferred C 0.35-0.55 0.37-0.50 Mn 0.6-1.2 0.7-0.9 Si0.9-2.5 1.3-2.1 P 0.01 max.  0.005 max. S 0.001 max.  0.0005 max. Cr0.75-2.0  1.2-1.5 Ni 3.5-7.0 3.7-4.5 Mo + ½ W 0.4-1.3 0.5-1.1 Cu 0.5-0.60.5-0.6 Co 0.01 max.  0.01 max. V + ( 5/9) × Nb 0.2-1.0 0.2-1.0 FeBalance BalanceIncluded in the balance are the usual impurities found in commercialgrades of steel alloys produced for similar use and properties. Withinthe foregoing weight percent ranges, silicon, copper, and vanadium arebalanced such that

2≦(% Si+% Cu)/(% V+(5/9)×% Nb)≦14.

The foregoing tabulation is provided as a convenient summary and is notintended to restrict the lower and upper values of the ranges of theindividual elements for use in combination with each other, or torestrict the ranges of the elements for use solely in combination witheach other. Thus, one or more of the ranges can be used with one or moreof the other ranges for the remaining elements. In addition, a minimumor maximum for an element of a broad or preferred composition can beused with the minimum or maximum for the same element in anotherpreferred or intermediate composition. Moreover, the alloy according tothe present invention may comprise, consist essentially of, or consistof the constituent elements described above and throughout thisapplication. Here and throughout this specification the term “percent”or the symbol “%” means percent by weight or mass percent, unlessotherwise specified.

In accordance with another aspect of the present invention, there isprovided a hardened and tempered steel alloy article that has very highstrength and fracture toughness. The article is formed from an alloyhaving the broad or preferred weight percent composition set forthabove. The alloy article according to this aspect of the invention isfurther characterized by being tempered at a temperature of about 500°F. to 600° F.

DETAILED DESCRIPTION

The alloy according to the present invention contains at least about0.35% and preferably at least about 0.37% carbon. Carbon contributes tothe high strength and hardness capability provided by the alloy. Carbonis also beneficial to the temper resistance of this alloy. Too muchcarbon adversely affects the toughness provided by the alloy. Therefore,carbon is restricted to not more than about 0.55%, better yet to notmore than about 0.50%, and preferably to not more than about 0.45%.

At least about 0.6%, better yet at least about 0.7%, and preferably atleast about 0.8% manganese is present in this alloy primarily todeoxidize the alloy. It has been found that manganese also benefits thehigh strength provided by the alloy. If too much manganese is present,then an undesirable amount of retained austenite may result duringhardening and quenching such that the high strength provided by thealloy is adversely affected. Therefore, the alloy contains not more thanabout 1.2% and preferably not more than about 0.9% manganese.

Silicon benefits the hardenability and temper resistance of this alloy.Therefore, the alloy contains at least about 0.9% silicon andpreferably, at least about 1.3% silicon. Too much silicon adverselyaffects the hardness, strength, and ductility of the alloy. In order toavoid such adverse effects silicon is restricted to not more than about2.5% and preferably to not more than about 2.1% in this alloy.

The alloy contains at least about 0.75% chromium because chromiumcontributes to the good hardenability, high strength, and temperresistance provided by the alloy. Preferably, the alloy contains atleast about 1.0%, and better yet at least about 1.2% chromium. More thanabout 2% chromium in the alloy adversely affects the impact toughnessand ductility provided by the alloy. Preferably, chromium is restrictedto not more than about 1.5% in this alloy and better yet to not morethan about 1.35%.

Nickel is beneficial to the good toughness provided by the alloyaccording to this invention. Therefore, the alloy contains at leastabout 3.5% nickel and preferably at least about 3.7% nickel. The benefitprovided by larger amounts of nickel adversely affects the cost of thealloy without providing a significant advantage. In order to limit theupside cost of the alloy, nickel is restricted to not more than about 7%and preferably to not more than about 4.5% in the alloy.

Molybdenum is a carbide former that is beneficial to the temperresistance provided by this alloy. The presence of molybdenum boosts thetempering temperature of the alloy such that a secondary hardeningeffect is achieved at about 500° F. Molybdenum also contributes to thestrength and fracture toughness provided by the alloy. The benefitsprovided by molybdenum are realized when the alloy contains at leastabout 0.4% molybdenum and preferably at least about 0.5% molybdenum.Like nickel, molybdenum does not provide an increasing advantage inproperties relative to the significant cost increase of adding largeramounts of molybdenum. For that reason, the alloy contains not more thanabout 1.3% molybdenum and preferably not more than about 1.1%molybdenum. Tungsten may be substituted for some or all of themolybdenum in this alloy. When present, tungsten is substituted formolybdenum on a 2:1 basis. When the alloy contains less than about 0.01%molybdenum, about 0.8 to about 2.6 percent, preferably about 1.0 to 2.2%tungsten is included to benefit the temper resistance, strength, andtoughness provided by the alloy.

This alloy preferably contains at least about 0.5% copper whichcontributes to the hardenability and impact toughness of the alloy. Toomuch copper can result in precipitation of an undesirable amount of freecopper in the alloy matrix and adversely affect the fracture toughnessof the alloy. Therefore, not more than about 0.6% copper is present inthis alloy.

Vanadium contributes to the high strength and good hardenabilityprovided by this alloy. Vanadium is also a carbide former and promotesthe formation of carbides that help provide grain refinement in thealloy and that benefit the temper resistance and secondary hardening ofthe alloy. For those reasons, the alloy preferably contains at leastabout 0.25% vanadium. Too much vanadium adversely affects the strengthof the alloy because of the formation of larger amounts of carbides inthe alloy which depletes carbon from the alloy matrix material.Accordingly, the alloy contains not more than about 0.35% vanadium.Niobium can be substituted for some or all of the vanadium in this alloybecause like vanadium, niobium combines with carbon to form M₄C₃carbides that benefit the temper resistance and hardenability of thealloy. When present, niobium is substituted for vanadium on 1.8:1 basis.When vanadium is restricted to not more than about 0.01%, the alloycontains about 0.2 to about 1.0% niobium.

This alloy may also contain a small amount of calcium up to about 0.005%retained from additions during melting of the alloy to help removesulfur and thereby benefit the fracture toughness provided by the alloy.

Silicon, copper, vanadium, and when present, niobium are preferablybalanced within their above-described weight percent ranges to benefitthe novel combination of strength and toughness that characterize thisalloy. More specifically, the ratio (% Si+% Cu)/(% V+(5/9)×% Nb) ispreferably about 2 to 14, and better yet, about 6 to 12. It is believedthat when the amounts of silicon, copper, and vanadium present in thealloy are balanced in accordance with the ratio, the grain boundaries ofthe alloy are strengthened by preventing brittle phases and trampelements from forming on the grain boundaries.

The balance of the alloy is essentially iron and the usual impuritiesfound in commercial grades of similar alloys and steels. In this regard,the alloy preferably contains not more than about 0.01%, better yet, notmore than about 0.005% phosphorus and not more than about 0.001%, betteryet not more than about 0.0005% sulfur. The alloy preferably containsnot more than about 0.01% cobalt. Titanium may be present at a residuallevel from deoxidation additions and is preferably restricted to notmore than about 0.01%.

Within the foregoing weight percent ranges, the elements can be balancedto provide different levels of tensile strength. Thus, for example, analloy composition containing about 0.38% C, 0.84% Mn, 1.51% Si, 1.25%Cr, 3.78% Ni, 0.50% Mo, 0.55% Cu, 0.29% V, balance essentially Fe, hasbeen found to provide a tensile strength in excess of 290 ksi incombination with a K_(Ic) fracture toughness greater than 80 ksi√in,after being tempered at about 500° F. for 3 hours. An alloy compositioncontaining about 0.40% C, 0.84% Mn, 1.97% Si, 1.26% Cr, 3.78% Ni, 1.01%Mo, 0.56% Cu, 0.30% V, balance essentially Fe, has been found to providea tensile strength in excess of 310 ksi in combination with a K_(Ic)fracture toughness greater than 60 ksi√in, after being tempered at about500° F. for 3 hours. Further, an alloy composition containing about0.50% C, 0.69% Mn, 1.38% Si, 1.30% Cr, 3.99% Ni, 0.50% Mo, 0.55% Cu,0.29% V, balance essentially Fe, has been found to provide a tensilestrength in excess of 340 ksi in combination with a K_(Ic) fracturetoughness greater than 30 ksi√in, after being tempered at about 300° F.for 2 ½ hours plus 2½ hours.

No special melting techniques are needed to make the alloy according tothis invention. The alloy is preferably vacuum induction melted (VIM)and, when desired as for critical applications, refined using vacuum arcremelting (VAR). It is believed that the alloy can also be arc melted inair. After air melting, the alloy is preferably refined by electroslagremelting (ESR) or VAR.

The alloy of this invention is preferably hot worked from a temperatureof about 2100° F. to form various intermediate product forms such asbillets and bars. The alloy is preferably heat treated by austenitizingat about 1585° F. to about 1635° F. for about 30 to 45 minutes. Thealloy is then air cooled or oil quenched from the austenitizingtemperature. The alloy is preferably deep chilled to either −100° F. or−320° F. for at least about one hour and then warmed in air. The alloyis preferably tempered at about 500° F. for about 3 hours and then aircooled. The alloy may be tempered at up to 600° F. when an optimumcombination of strength and toughness is not required.

The alloy of the present invention is useful in a wide range ofapplications. The very high strength and good fracture toughness of thealloy makes it useful for machine tool components and also in structuralcomponents for aircraft, including landing gear. The alloy of thisinvention is also useful for automotive components including, but notlimited to, structural members, drive shafts, springs, and crankshafts.It is believed that the alloy also has utility in armor plate, sheet,and bars.

Working Examples

Seven 35-lb. VIM heats were produced for evaluation. The weight percentcompositions of the heats are set forth in Table 1 below. All heats weremelted using ultra-clean raw materials and used calcium as adesulfurizing addition. The heats were cast as 4 in. square ingots. Theingots were forged to 2¼ in. square bars from a starting temperature ofabout 2100° F. The bars were cut to shorter lengths and half of theshorter length bars were further forged to 1 in. square bars, again froma starting temperature of 2100° F. The 1 in. bars were cut to stillshorter lengths which were forged to ¾ in. square bars from 2100° F.

The ¾ in. square bars and the remainder of the 2¼ in. square bars wereannealed at 1050° F. for 6 hours and then cooled in air to roomtemperature. Standard specimens for tensile testing and standardspecimens for Charpy V-notch impact testing were prepared from the ¾ in.bars of each heat. Standard compact tension blocks for fracturetoughness testing were prepared from the 2½ in. square bars of eachheat. All of the specimens were heat treated at 1585° F. for 30 minutesand then air cooled. The test specimens were then chilled at −100° F.for 1 hour and warmed in air to room temperature. Duplicate specimens ofeach heat were then tempered at one of three different temperatures,400° F., 500° F., and 600° F., by holding at the respective temperaturefor 3 hours. The tempered specimens were then air cooled to roomtemperature.

TABLE I 1509 1483 1484 1485 1486 1487 1488 C 0.36 0.35 0.37 0.36 0.370.41 0.44 Mn 0.83 0.83 0.83 0.84 0.84 0.84 0.83 Si 0.95 0.94 0.92 1.201.48 0.96 0.95 P <0.005 <0.005 <0.005 <0.005 <0.005 <0.005 <0.005 S<0.0005 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 Cr 1.26 1.281.25 1.25 1.26 1.26 1.26 Ni 3.76 3.78 3.76 3.78 3.77 3.75 3.78 Mo <0.010.20 0.49 <0.01 <0.01 <0.01 <0.01 Cu 0.55 0.55 0.54 0.55 0.55 0.55 0.55V 0.30 0.29 0.29 0.29 0.30 0.29 0.30 Ca 0.0014 0.0013 0.002 0.00150.0014 0.0021 0.0017 Fe Bal.¹ Bal.¹ Bal.¹ Bal.¹ Bal.¹ Bal.¹ Bal.¹ ¹Thebalance includes usual impurities.

The results of mechanical, Charpy V-notch, and fracture toughnesstesting on the tempered specimens are presented in Table II belowincluding the 0.2% Offset Yield Strength (Y.S.) and Ultimate TensileStrength (U.T.S.) in ksi, the percent elongation (Elong.), the percentreduction in area (R.A.), the Charpy V-notch impact energy (CVN I.E.) inft-lbs, and the K_(Ic) fracture toughness (K_(Ic)) in ksi√in.

TABLE II Temper Temp. Y.S. U.T.S. Elong. R.A. CVN I.E. KIc Heat No. (F.)Sample (ksi) (ksi) (%) (%) (ft-lbs.) (ksi√in.) 1509 400 A1 232.6 277.511.5 46.1 24.5 92.2 A2 226.9 269.8 12.8 51.8 25.4 92.7 Avg. 229.7 273.612.2 49.0 25.0 92.5 500 B1 235.4 275.9 10.9 51.3 24.3 90.1 B2 235.3275.4 10.9 50.2 23.2 94.3 Avg. 235.3 275.6 10.9 50.7 23.8 92.2 600 C1234.4 269.1 10.9 50.8 20.6 89.0 C2 235.1 269.9 10.9 50.8 21.8 84.7 Avg.234.8 269.5 10.9 50.8 21.2 86.9 1483 400 A1 230.1 277.2 12.2 50.1 25.799.4 A2 234.2 280.9 12.4 50.2 25.5 99.9 Avg. 232.1 279.1 12.3 50.2 25.699.7 500 B1 236.8 276.1 11.5 50.8 21.3 95.8 B2 239.4 277.9 10.5 46.221.6 93.9 Avg. 238.1 277.0 11.0 48.5 21.5 94.9 600 C1 240.1 272.3 11.952.8 19.4 90.4 C2 240.6 273.4 11.0 51.2 18.8 90.9 Avg. 240.3 272.8 11.552.0 19.1 90.7 1484 400 A1 234.9 279.9 12.1 50.1 22.7 96.9 A2 235.8280.4 11.7 49.0 23.5 97.9 Avg. 235.3 280.1 11.9 49.6 23.1 97.4 500 B1239.4 278.4 11.2 50.6 21.9 96.8 B2 241.2 280.5 10.9 47.2 22.7 94.8 Avg.240.3 279.5 11.1 48.9 22.3 95.8 600 C1 243.4 277.1 11.1 50.5 18.6 91.2C2 239.6 272.8 10.6 48.9 17.9 91.4 Avg. 241.5 275.0 10.9 49.7 18.3 91.31485 400 A1 234.2 282.5 12.7 50.1 23.1 97.3 A2 231.0 279.5 13.2 52.321.9 98.3 Avg. 232.6 281.0 13.0 51.2 22.5 97.8 500 B1 236.2 276.1 11.450.5 21.0 94.1 B2 236.7 276.5 11.3 48.7 21.2 96.9 Avg. 236.4 276.3 11.449.6 21.1 95.5 600 C1 242.5 274.4 11.3 48.7 20.6 91.2 C2 242.1 275.112.1 51.5 20.8 88.7 Avg. 242.3 274.8 11.7 50.1 20.7 90.0 1486 400 A1232.4 281.9 12.1 50.6 23.9 86.6 A2 233.9 283.0 12.0 51.0 21.6 91.5 Avg.233.2 282.4 12.1 50.8 22.8 89.1 500 B1 238.3 280.2 11.6 50.6 19.9 91.6B2 240.4 282.1 11.4 51.0 19.5 85.6 Avg. 239.3 281.1 11.5 50.8 19.7 88.6600 C1 242.9 277.9 11.4 49.9 19.0 88.7 C2 244.1 279.6 11.1 51.5 18.488.3 Avg. 243.5 278.7 11.3 50.7 18.7 88.5 1487 400 A1 246.5 296.8 12.346.0 17.8 66.6 A2 247.1 294.9 12.0 47.1 14.8 68.1 Avg. 246.8 295.9 12.246.6 16.3 67.4 500 B1 252.0 292.5 10.7 47.7 15.6 70.4 B2 253.0 293.410.2 44.5 14.1 71.4 Avg. 252.5 293.0 10.5 46.1 14.9 70.9 600 C1 251.6285.6 10.1 46.5 16.2 68.8 C2 252.4 284.7 10.8 47.1 15.2 64.7 Avg. 252.0285.1 10.5 46.8 15.7 66.8 1488 400 A1 253.2 305.2 10.9 42.4 14.8 52.6 A2254.9 306.8 10.9 42.3 15.3 59.5 Avg. 254.1 306.0 10.9 42.4 15.1 56.1 500B1 262.3 304.1 9.7 44.6 15.4 54.3 B2 262.2 304.7 9.7 43.4 14.9 57.6 Avg.262.3 304.4 9.7 44.0 15.2 56.0 600 C1 259.8 295.7 10.0 44.8 14.8 50.1 C2261.6 297.5 10.0 44.7 14.5 49.8 Avg. 260.7 296.6 10.0 44.8 14.7 50.0

The data presented in Table II show that Heat 1484, which has a weightpercent composition in accordance with the alloy described herein, isthe only alloy composition that provides a tensile strength of 280 ksiand a fracture toughness of at least 90 ksi√in after tempering a 500° F.

The terms and expressions which are employed herein are used as terms ofdescription and not of limitation. There is no intention in the use ofsuch terms and expressions of excluding any equivalents of the featuresshown and described or portions thereof. It is recognized that variousmodifications are possible within the invention described and claimedherein.

1. A high strength, high toughness steel alloy having good temperresistance, said alloy comprising, in weight percent, about: Carbon0.35-0.5  Manganese 0.6-1.2 Silicon 0.9-2.5 Phosphorus 0.01 max. Sulfur0.001 max.  Chromium 1.0-1.5 Nickel 3.5-4.5 Molybdenum 0.4-1.3 Copper0.5-0.6 Cobalt 0.01 max. Vanadium 0.25-0.35

the balance being iron and usual impurities, and wherein2≦(% Si+% Cu)/% V≦14.
 2. The alloy as claimed in claim 1 which containsat least about 0.37% carbon.
 3. The alloy as claimed in claim 2 whichcontains not more than about 0.45% carbon.
 4. The alloy as claimed inclaim 1 which contains at least about 1.3% silicon.
 5. The alloy asclaimed in claim 4 which contains not more than about 2.1% silicon. 6.The alloy as claimed in claim 1 which contains at least about 3.7%nickel.
 7. The alloy as claimed in claim 6 which contains not more thanabout 4.2% nickel.
 8. The alloy as claimed in claim 1 which contains atleast about 0.5% molybdenum.
 9. The alloy as claimed in claim 8 whichcontains not more than about 1.1% molybdenum.
 10. The alloy as claimedin claim 1 which contains at least about 1.2% chromium.
 11. The alloy asclaimed in claim 10 which contains not more than about 1.35% chromium.12. The alloy as claimed in claim 1 wherein 6≦(% Si+% Cu)/% V≦12.
 13. Ahigh strength, high toughness steel alloy having good temper resistance,said alloy comprising, in weight percent, about: Carbon 0.37-0.45Manganese 0.7-0.9 Silicon 1.3-2.1 Phosphorus  0.005 max. Sulfur 0.0005max. Chromium  1.2-1.35 Nickel 3.7-4.2 Molybdenum 0.5-1.1 Copper 0.5-0.6Cobalt  0.01 max. Vanadium 0.25-0.35

the balance being iron and usual impurities, and wherein6≦(% Si+% Cu)/% V≦12.
 14. A hardened and tempered alloy article that hasvery high strength and fracture toughness, said article comprising analloy consisting essentially of, in weight percent, about Carbon0.35-0.5  Manganese 0.6-1.2 Silicon 1.3-2.5 Phosphorus 0.01 max. Sulfur0.001 max.  Chromium 1.0-1.5 Nickel 3.5-4.5 Molybdenum 0.4-1.3 Copper0.5-0.6 Cobalt 0.01 max. Vanadium 0.25-0.35

the balance being iron and usual impurities; wherein 2≦(% Si+% Cu)/%V≦14; said article having been tempered at a temperature of about 500°F. to 600° F.
 15. The alloy article as claimed in claim 14 whichcontains at least about 0.37% carbon.
 16. The alloy article as claimedin claim 15 which contains not more than about 0.45% carbon.
 17. Thealloy article as claimed in claim 14 which contains at least about 1.3%silicon.
 18. The alloy article as claimed in claim 17 which contains notmore than about 2.1% silicon.
 19. The alloy article as claimed in claim14 which contains at least about 3.7% nickel.
 20. The alloy article asclaimed in claim 19 which contains not more than about 4.2% nickel. 21.The alloy article as claimed in claim 14 which contains at least about0.5% molybdenum.
 22. The alloy article as claimed in claim 21 whichcontains not more than about 1.1% molybdenum.
 23. The alloy article asclaimed in claim 14 which contains at least about 1.2% chromium.
 24. Thealloy article as claimed in claim 23 which contains not more than about1.35% chromium.
 25. The alloy article as claimed in claim 14 wherein6≦(% Si+% Cu)/% V≦12.
 26. A hardened and tempered alloy article that hasvery high strength and fracture toughness, said article comprising analloy consisting essentially of, in weight percent, about Carbon0.37-0.45 Manganese 0.7-0.9 Silicon 1.3-2.1 Phosphorus  0.005 max.Sulfur 0.0005 max. Chromium  1.2-1.35 Nickel 3.7-4.2 Molybdenum 0.5-1.1Copper 0.5-0.6 Cobalt  0.01 max. Vanadium 0.25-0.35

the balance being iron and usual impurities; wherein 6≦(% Si+% Cu)/%V≦12; said article having been tempered at a temperature of about 500°F. to 600° F.
 27. A high strength, high toughness steel alloy havinggood temper resistance, said alloy comprising, in weight percent, about:C 0.35-0.55 Mn 0.6-1.2 Si 0.9-2.5 P 0.01 max. S 0.001 max.  Cr 0.75-2.0 Ni 3.5-7.0 Mo + ½ W 0.4-1.3 Cu 0.5-0.6 Co 0.01 max. V + ( 5/9) × Nb0.2-1.0

the balance being iron and usual impurities, and wherein2≦(% Si+% Cu)/(% V+(5/9)×% Nb)≦14.
 28. The alloy as claimed in claim 27which contains at least about 0.37% carbon.
 29. The alloy as claimed inclaim 28 which contains not more than about 0.45% carbon.
 30. The alloyas claimed in claim 27 which contains at least about 1.3% silicon. 31.The alloy as claimed in claim 30 which contains not more than about 2.1%silicon.
 32. The alloy as claimed in claim 27 which contains at leastabout 3.7% nickel.
 33. The alloy as claimed in claim 32 which containsnot more than about 4.2% nickel.
 34. The alloy as claimed in claim 27which contains at least about 0.5% molybdenum.
 35. The alloy as claimedin claim 34 which contains not more than about 1.1% molybdenum.
 36. Thealloy as claimed in claim 27 which contains at least about 1.2%chromium.
 37. The alloy as claimed in claim 36 which contains not morethan about 1.35% chromium.
 38. The alloy as claimed in claim 1 wherein6≦(% Si+% Cu)/(% V+(5/9)×% Nb)≦12.
 39. A high strength, high toughnesssteel alloy having good temper resistance, said alloy comprising, inweight percent, about: C 0.37-0.50 Mn 0.7-0.9 Si 1.3-2.1 P  0.005 max. S0.0005 max. Cr 1.0-1.5 Ni 3.7-4.5 Mo + ½ W 0.5-1.1 Cu 0.5-0.6 Co  0.01max. V + ( 5/9) × Nb 0.2-1.0

the balance being iron and usual impurities, and wherein6≦(% Si+% Cu)/(% V+(5/9)×% Nb)≦12.
 40. A hardened and tempered alloyarticle that has very high strength and fracture toughness, said articlecomprising an alloy consisting essentially of, in weight percent, aboutC 0.35-0.55 Mn 0.6-1.2 Si 1.3-2.5 P 0.01 max. S 0.001 max.  Cr 0.75-2.0 Ni 3.5-7.0 Mo + ½ W 0.4-1.3 Cu 0.5-0.6 Co 0.01 max. V + ( 5/9) × Nb0.2-1.0

the balance being iron and usual impurities; wherein 2≦(% Si+% Cu)/(%V+(5/9)×% Nb)≦14; said article having been tempered at a temperature ofabout 500° F. to 600° F.
 41. The alloy article as claimed in claim 40which contains at least about 0.37% carbon.
 42. The alloy article asclaimed in claim 41 which contains not more than about 0.45% carbon. 43.The alloy article as claimed in claim 40 which contains at least about1.3% silicon.
 44. The alloy article as claimed in claim 43 whichcontains not more than about 2.1% silicon.
 45. The alloy article asclaimed in claim 40 which contains at least about 3.7% nickel.
 46. Thealloy article as claimed in claim 45 which contains not more than about4.2% nickel.
 47. The alloy article as claimed in claim 40 which containsat least about 0.5% molybdenum.
 48. The alloy article as claimed inclaim 47 which contains not more than about 1.1% molybdenum.
 49. Thealloy article as claimed in claim 40 which contains at least about 1.2%chromium.
 50. The alloy article as claimed in claim 49 which containsnot more than about 1.35% chromium.
 51. The alloy article as claimed inclaim 40 wherein 6≦(% Si+% Cu)/(% V+(5/9)×% Nb)≦12.
 52. A hardened andtempered alloy article that has very high strength and fracturetoughness, said article comprising an alloy consisting essentially of,in weight percent, about C 0.37-0.50 Mn 0.7-0.9 Si 1.3-2.1 P  0.005 max.S 0.0005 max. Cr 1.0-1.5 Ni 3.7-4.5 Mo + ½ W 0.5-1.1 Cu 0.5-0.6 Co  0.01max. V + ( 5/9) × Nb 0.2-1.0

the balance being iron and usual impurities; wherein 6≦(% Si+% Cu)/(%V+(5/9)×% Nb)≦12; said article having been tempered at a temperature ofabout 500° F. to 600° F.
 53. A high strength, high toughness steel alloyhaving good temper resistance, said alloy consisting essentially of, inweight percent, about: C 0.35-0.50 Mn 0.6-1.2 Si 0.9-2.5 P 0.01 max. S0.001 max.  Cr 0.75-2.0  Ni 3.5-7.0 Mo 0.01 max. W 0.8-2.6 Cu 0.5-0.6 Co0.01 max. Nb 0.2-1.0 V 0.01 max.

the balance being iron and usual impurities, and wherein2≦(% Si+% Cu)/% Nb≦14.
 54. The alloy as claimed in claim 53 whichcontains at least about 0.37% carbon.
 55. The alloy as claimed in claim54 which contains not more than about 0.45% carbon.
 56. The alloy asclaimed in claim 53 which contains at least about 1.3% silicon.
 57. Thealloy as claimed in claim 56 which contains not more than about 2.1%silicon.
 58. The alloy as claimed in claim 53 which contains at leastabout 3.7% nickel.
 59. The alloy as claimed in claim 58 which containsnot more than about 4.2% nickel.
 60. The alloy as claimed in claim 59which contains at least about 0.5% molybdenum.
 61. The alloy as claimedin claim 60 which contains not more than about 1.1% molybdenum.
 62. Thealloy as claimed in claim 53 which contains at least about 1.0%tungsten.
 63. The alloy as claimed in claim 62 which contains not morethan about 2.2% tungsten.
 64. The alloy as claimed in claim 53 whichcontains at least about 1.0% chromium.
 65. The alloy as claimed in claim64 which contains not more than about 1.5% chromium.
 66. The alloy asclaimed in claim 53 which contains at least about 0.2% niobium.
 67. Thealloy as claimed in claim 66 which contains not more than about 1.0%niobium.
 68. The alloy as claimed in claim 53 wherein 6≦(% Si+% Cu)/%Nb≦12.
 69. A high strength, high toughness steel alloy having goodtemper resistance, said alloy consisting essentially of, in weightpercent, about: C 0.37-0.50 Mn 0.7-0.9 Si 1.3-2.1 P 0.005 max.  S 0.0005max.  Cr 1.0-1.5 Ni 3.7-4.5 Mo 0.01 max. W 1.0-2.2 Cu 0.5-0.6 Co 0.01max. Nb 0.2-1.0 V 0.01 max.

the balance being iron and usual impurities, and wherein6≦(% Si+% Cu)/% Nb≦12.
 70. A hardened and tempered alloy article thathas very high strength and fracture toughness, said article comprisingan alloy consisting essentially of, in weight percent, about C 0.35-0.55Mn 0.6-1.2 Si 1.3-2.5 P 0.01 max. S 0.001 max.  Cr 0.75-2.0  Ni 3.5-7.0Mo 0.01 max. W 0.8-2.6 Cu 0.5-0.6 Co 0.01 max. Nb 0.2-1.0 V 0.01 max.

the balance being iron and usual impurities; wherein 2≦(% Si+% Cu)/%Nb≦14; said article having been tempered at a temperature of about 500°F. to 600° F.
 71. The alloy article as claimed in claim 70 whichcontains at least about 0.37% carbon.
 72. The alloy article as claimedin claim 71 which contains not more than about 0.45% carbon.
 73. Thealloy article as claimed in claim 70 which contains at least about 1.3%silicon.
 74. The alloy article as claimed in claim 73 which contains notmore than about 2.1% silicon.
 75. The alloy article as claimed in claim70 which contains at least about 3.7% nickel.
 76. The alloy article asclaimed in claim 75 which contains not more than about 4.2% nickel. 77.The alloy article as claimed in claim 70 which contains at least about0.5% molybdenum.
 78. The alloy article as claimed in claim 77 whichcontains not more than about 1.1% molybdenum.
 79. The alloy article asclaimed in claim 70 which contains at least about 1.0% tungsten.
 80. Thealloy article as claimed in claim 79 which contains not more than about2.2% tungsten.
 81. The alloy article as claimed in claim 70 whichcontains at least about 1.0% chromium.
 82. The alloy article as claimedin claim 81 which contains not more than about 1.5% chromium.
 83. Thealloy article as claimed in claim 70 which contains at least about 0.2%niobium.
 84. The alloy article as claimed in claim 83 which contains notmore than about 1.0% niobium.
 85. The alloy article as claimed in claim70 wherein 6≦(% Si+% Cu)/% Nb≦12.
 86. A hardened and tempered alloyarticle that has very high strength and fracture toughness, said articlecomprising an alloy consisting essentially of, in weight percent, aboutC 0.37-0.50 Mn 0.7-0.9 Si 1.3-2.1 P 0.005 max.  S 0.0005 max.  Cr1.0-1.5 Ni 3.7-4.5 Mo 0.01 max. W 1.0-2.2 Cu 0.5-0.6 Co 0.01 max. Nb0.2-1.0 V 0.01 max.

the balance being iron and usual impurities; wherein 6≦(% Si+% Cu)/%Nb≦12; said article having been tempered at a temperature of about 500°F. to 600° F.